The invention concerns a control and regulating device for a needle element of a hot or cold channel of a plastic molding tool, wherein rotation of a drive device is converted by means of a converting device into an axial movement of the needle element
Such control and regulating devices are known for example from U.S. Pat. No. 5,078,589 or U.S. Pat. No. 5,238,378. The converting devices provided in those known control and regulating devices, for converting rotation of a drive device into an axial movement of the needle element, have a screw and nut element of constant pitch. That constant pitch of the screw and nut element determines the movements of the needle element of the hot or cold channel of the corresponding plastic molding tool.
Demands for up-to-date processing of injection-moldable plastic materials with their individual process-specific and physical criteria to provide the respective plastic moldings are not satisfied or are only inadequately satisfied or are only satisfied by virtue of a suitable compromise, in regard to fastest possible production cycles, dealing carefully with the injection molding materials, that is to say injection-moldable plastic materials, dealing carefully with the molding tools, an optimum injection molding process control, making use of motor-driven drive devices and reducing the level of wear of the respective needle element or the drive device with such screw and nut elements of constant pitch.
Admittedly, small or normal pitches of the screw and nut element involve a high force and a very substantial self-locking action when pressure is applied or in terms of needle locking, as well as fine adjustability, but they suffer from the disadvantage that the respective no-load or idle stroke of the needle element is highly time-intensive and that possible process regulation can be effected only very sluggishly, that is to say involving a great deal of time. That time penalty puts a load on the operating cycle and increases costs in the above-mentioned idle stroke range for example for opening the needle element for the fastest possible quantitative through-flow of the plastic material, as for example hot channel needle elements can have a needle stroke of between 8 and 16 mm or more. Consequently, when the screw and nut element involve small pitches, reactive oscillation as rapidly as possible is not adequately afforded for process regulation purposes so that the efficiency of the regulating device which usually involves an electronic regulating device is not put to use or is not completely put to use. The respectively desired level of quality of production of the respective plastic pars can consequently not be kept stable or stabilised.
Admittedly, a fast movement of the needle element in the idle stroke range can be implemented with a greater or high pitch for the screw and nut clement of the converting device of known control and regulating devices for a needle clement of a hot or cold channel of a plastic molding tool, but during the process control phase the needle element becomes over-active, whereby necessary fine actuation becomes more difficult. In addition such an increased or high pitch results in an increased need for counter-holding force, which means that the expenditure in terms of energy and power is correspondingly increased. A further deficiency of such an increased or large pitch is that so-called spot-wise grinding-in of the needle element as a closure element of the runner region to the mold cavity causes considerable tool wear and is relatively force-less as the self-locking action of the needle element is at least greatly reduced as a consequence of the increased or great pitch of the screw and nut elements.
DE 196 11 880 A1 discloses an injection molding tool with a plurality of hot channel needle closure nozzles which are connected to an actuating device for the simultaneous actuation of a plurality of needle That known injection molding tool has a mechanical drive transmission between a stroke drive and needle carrier elements arranged at the individual needles. Elastic intermediate elements are provided between the needle carrier elements and the respective needle. Transversely with respect to the longitudinal extent of the needles, it is possible to provide a slider connected to the stroke drive, as the rigid mechanical drive transmission. The elastic intermediate elements used can be compression springs which are preferably in the form of diaphragm springs. The slider and/or the needle carrier elements can have inclined guides for converting the slider stroke movement into the working movement of the needles, which working movement is transverse with respect to the slider movement
The object of the invention is to provide a control and regulating device of the kind set forth in the opening part of this specification, in which the opening and closing times of the needle element are reduced, but at the same time fine control is possible.
The foregoing object is achieved by providing a converting device which has at least one slide path and a feeler or follower element which is guided on the slide path, wherein the at least one slide path is provided on a slide path surface which is concentric with respect to the center line of the needle element.
In consideration of those factors, the object of the invention is to provide a control and regulating device of the kind set forth in the opening part of this specification, which so-to-speak combines together the advantages of a low and a high pitch and eliminates the disadvantages thereof.
In a control and regulating device of the kind set forth in the opening part of this specification, in accordance with the invention that object is attained in that the converting device has at least one slide path and a feeler or follower element which is guided on the slide path, wherein the at least one slide path is provided on a slide path surface which is concentric with respect to the center line of the needle element.
The at least one slide path can be of optimum design in a simple manner and can be individually configured as desired in order to permit the desired axial movement of the needle element, that is to say as desired a rapid idle stroke movement and a process regulation and deceleration movement of the needle element, which is slow in comparison therewith. The needle element may involve a needle element of a full cross-section, a hollow needle combined with such a needle element, for example of a compression needle unit, or the like. Such needle elements or control and regulating devices for a hot or cold channel of a plastic molding tool are described in the present applicant""s prior patent application Ser. No. 198 57 735. The control and regulating device according to the invention is suitable by way of example for all needle elements or molding tools described in said prior patent application.
The at least one slide path of the converting device of the control and regulating device according to the invention can in this case extend over an angle of 360 degrees of angle or more, around the center line of the needle element. It may be advantageous if two or more slide paths are provided distributed uniformly around the center line of the needle element in order, with a rotation of the drive device through a small angle, to produce the desired axial displacement of the needle element. That small rotary angle is dependent on the number of slide paths, that is to say inversely proportional to the number of slide paths. With two slide paths the rotary angle can be 180 degrees or less than 180 degrees. With three slide paths the rotary angle can be 120 degrees or slightly less. Implementation of the smallest possible rotary angle is also dependent on the diameter of the slide path surface for the slide paths. The greater that diameter is, the correspondingly greater can be the number of slide paths, that is to say the correspondingly smaller can be said rotary angle. A small rotary movement of the drive device affords the advantage that, for example when using a worm drive with an extreme transmission ratio, the speed of rotation of the drive worm can be drastically reduced, thereby resulting in a corresponding time saving. The sane applies also for example for chain, toothed belt and gear drives as well as in relation to toothed rack versions and the like, in which respect the rotary speed or the piston stroke movement can be drastically reduced. In additionxe2x80x94for example in clean-room production of plastic articlesxe2x80x94it is possible to use electrical stepping or servo motors which have a high torque and which if required rotate at low speed and which afford very rapid reaction options. During the corresponding slight rotary movement, the entire axial stroke movement of the needle element is performed, that is to say the idle stroke movement and the process regulation and deceleration movement.
In accordance with the invention the at least one slide path can be provided in a rotatably mounted sleeve element which has the slide path surface and which is operatively connected to the drive device. In this case the at least one slide path can be provided on the internal surface of the sleeve element, which forms the slide path surface.
The sleeve element with the at least one slide path can be axially immovably rotatably supported and provided with a drive output gear with which a drive gear is in meshing engagement. The drive output gear may involve for example a worm gear. The drive gear is then a worm spindle.
The needle element can be provided non-rotatably in the case of such a control and regulating device of the above-described kind, and can have at least one radially projecting feeler or follower element.
Another possibility provides that the sleeve element with the needle element forms a rigid unit and is axially displaceable and rotatable about the center line of the needle element and that the at least one follower element is provided non-rotatably and axially immovably. This last-described alternative configuration involves so-to-speak a reversal of the control and regulating device or converting device, as described hereinbefore.
Likewise it is possible for the at least one slide path to be provided in a portion of the needle element which is disposed non-rotatably and for the at least one follower element to project from the rotatable sleeve element. This also involves only a reversal of the principle according to the invention of the converting device of the control and regulating device according to the invention.
In accordance with the invention the at least one follower element can be formed by a cylinder, a roller or a pin. In order to withstand very high counter pressures or counter forces in a wear-resistant manner, the at least one pin can be provided with a curved or cambered flattened sliding surface. A sliding surface of such a configuration provides for a reduced pressure in relation to surface area, which results in a corresponding reduction in wear.
In the case of the control and regulating device according to the invention, it is preferable if the at least one slide path has a fast-displacement portion of large pitch and an adjoining process regulation and deceleration portion of comparatively small pitch. Independent patent protection is requested in that respect.
It is preferred in this case if the process regulation and deceleration portion, on the side remote from the fast-displacement portion, is adjoined by a self-locking portion. The self-locking portion is preferably of a zero pitch.
In order in the event of over-control of the drive device to ensure that the at least one follower element is not separated from or moved away from the associated slide path, it is desirable if the fast-displacement portion, on the side from the process regulation and deceleration portion, is adjoined by a catch hook portion.
Desirably, provided between each of the individual slide path portions of the at least one slide path is a respective rounded slide curve portion in order to achieve a suitable movement of the follower element on the slide path and consequently a corresponding movement of the associated needle element.
In accordance with the invention the at least one slide path can be provided with mutually parallel slide path surfaces. In the case of such a design configuration, at least two slot-shaped slide paths can be provided on the slide path surface which is concentric with respect to the center line of the needle element, being equidistantly spaced in the peripheral direction of the slide path surface. In this arrangement, the at least two slot-shaped slide paths are provided separately from each other in the peripheral direction of the slide path surface. It is however also possible for the at least two slot-shaped slide paths to be respectively connected together by means of a needle return portion. In the first-mentioned case with mutually separated slot-shaped slide paths, it is necessary for the drive device to be driven with a reciprocating motion in order to move the needle element forward and back, while in the case of the structure in which the slot-shaped slide paths are respectively connected together by means of a needle return portion, it is possible for the drive device to be rotated only in one direction and in that situation to successively implement the closing and opening movement of the needle element.
An advantage of the configuration according to the invention of the control and regulating device with at least two slot-shaped slide paths which are respectively connected together by means of a needle return portion, that is to say which extend closed in themselves around the slide path surface, is that the needle return portion can be of a pitch which can be greater than the pitch of the fast-displacement portion so that, with a constant drive or angular speed of the drive device, the needle return motion takes place still faster than the fast-displacement motion, that is to say the fast feed motion of the needle element which is followed by the process regulation and deceleration movement of the needle element.
Another possible configuration of the control and regulating device according to the invention provides that the at least one slide path has two slide surfaces which are disposed in diametrally and also axially opposite relationship on the slide path surface and which are arranged to extend in mutually parallel relationship, wherein an associated portion of the follower element bears in guided relationship against each of the two slide surfaces. This embodiment of the control and regulating device according to the invention also provides that it is possible to have more than one slide path with two respective diametrally and axially oppositely disposed slide surfaces which are arranged to extend in mutually parallel relationship, wherein a portion of the associated follower element bears in guided relationship against each of the slide surfaces which are disposed in paired diametrally and axially opposite relationship. Those diametrally and axially oppositely disposed slide surfaces of the at least one slide track are each axially accessible from one side or the other so that in each case thereforexe2x80x94in contrast to the above-described slot-shaped slide pathsxe2x80x94this arrangement affords open slide paths. That can be desirable from points of view involving manufacture.
A farther simplified variant, that is to say which is even easier to manufacture, of the control and regulating device according to the invention, is characterised in that the at least one slide path has a single slide surface, against which the associated follower element or the associated follower element portion is urged by means of a spring device. In this case at least two slide paths can be provided separatedly from each other in the peripheral direction on the slide path surface which is concentric with respect to the center line of the needle element, the at least two slide paths each having a single slide surface. With this design configuration it is necessary for the drive device to be driven with a reciprocating movement in order to move the needle element forward and back.
It is however also possible for the slide surfaces of the at least two slide paths of the last-described alternative configuration to be respectively connected together by means of a needle return portion so as to provide a slide path which is closed in itself and which extends around the slide path surface. With this design configuration it is possible for the drive device to be driven only in one direction of rotation and for the needle element to be axially reciprocated. So that with such a design configuration of the last-mentioned kind, with a constant speed of rotation of the drive device, the needle return movement can also be effected at a higher speed than the fast displacement of the needle element, the needle return portion can be of a pitch which is greater than the pitch of the fast-displacement portion.
The last-described embodiment of the control and regulating device according to the invention with at least one slide path having a single slide surface against which the follower element is urged by means of a spring device therefore involves an open slide path which can be precisely manufactured in a simple manner, unlike a slot-shaped slide path.